The assay of biochemicals, such as glucose and lactate, is important in medicine, biotechnology, and food processing (dairy and wine). Monitoring of glucose concentrations in fluids of the human body is of particular relevance to diabetes management. Monitoring of lactate in fluids of the human body is of relevance to diagnosis of trauma, of myocardial infarction, congestive heart failure, pulmonary edema, septicemia, hemorrhage, and others. Blood lactate levels above 7-8 mM are indicative of a fatal outcome. Bedside analyzers of lactate are useful in determining the response of patients to treatment, while in accidents and battle, they are useful in triage. Glucose assays are common in clinical practice and are applied in the diagnosis of Diabetes Mellitus and its management. Continuously or intermittently operating glucose sensors, including sensors implanted in the human body, are sought for the management of Type I diabetes, for example, for warning of imminent or actual hypoglycemia and its avoidance. Hypoglycemia can be fatal. For maintenance of diabetic patients at or near normal blood glucose levels, frequent or continuous monitoring of glucose is needed. Today, most Type I diabetic patients maintain their blood glucose at higher than normal levels, so as to reduce risk of fatal hypoglycemia. This is undesirable, as maintenance of higher than normal blood glucose levels has been shown to be a leading cause of blindness, kidney failure, neuropathy, and other complications of diabetes. It would, therefore, be useful to provide a glucose sensor that operates continuously or intermittently for a prolonged period of time to measure glucose in body fluid at 37.degree. C. without substantial loss of sensitivity.
The present invention discloses material, structures, and methods enabling continuous operation of electrochemical sensors, for example, measuring glucose for more than one week or measuring lactate for more than 100 hours, with less than 10% loss in sensitivity.